Arc fault and ground fault interrupter using dual adc

ABSTRACT

Method and system for performing arc fault and ground fault detection in a dual function CAFI/GFCI circuit breaker uses two analog-to-digital converters (ADC), one for performing arc fault sampling and one for performing ground fault sampling. Each ADC operates independently of the other ADC and may be accessed as needed by the microcontroller without interfering with the operation of the other ADC. Such simultaneous use of multiple ADCs minimizes or eliminates the need for complex time slicing and similar control schemes, thus freeing up the microcontroller for other operations and fault detection related tasks.

FIELD OF INVENTION

The embodiments disclosed herein relate generally to methods and systemsfor protecting against ground faults and arc faults, and particularly toa method and system for protecting against ground faults and arc faultsthat employ a microcontroller and separate analog-to-digital converters(ADC).

BACKGROUND OF INVENTION

Ground fault circuit interrupters (GFCI) and arc fault circuitinterrupters (AFCI) are well known in the art. A GFCI is designed todetect a ground fault, which is an unintended conductive path between anungrounded current carrying conductor and ground. The term “groundfault” generally includes both a “ground-fault” and a “grounded-neutralfault.” Ground-faults may be detected by sampling the current in a sensecircuit on the secondary side of a transformer during a designated timeinterval and comparing the samples to a reference value. The sampling ofthe current is typically done by an ADC and involves conversion of thecurrent from a continuous analog signal to digital data.Grounded-neutral faults may be detected by injecting current into thesense circuit during a separate time interval to produce a decayingsinusoidal signal in the sense circuit, then sampling the sinusoidalsignal to determine the presence of a grounded-neutral fault.

An AFCI on the other hand, is designed to detect electrical arcing orarc faults. Arc faults are usually intermittent and do not generatesustained currents of sufficient magnitude to trip a conventionalcircuit breaker, so inputs such as band-pass filters, line currentsensors, and voltage sensors must be sampled at regular intervals inorder to detect an arc fault. Presently, combination arc fault circuitinterrupters (CAFI) are available that can detect both parallel arcing(i.e., arcing between two conductors or between a conductor and ground)and series arcing (i.e., arcing across a break in a conductor, such as adamaged electrical cord).

Attempts to integrate CAFI and GFCI into a single, dual functionCAFI/GFCI circuit breaker have met with mixed results. This is because,as a general rule, design strategies stress using a bare minimum numberof components to achieve a desired function. Accordingly, most dualfunction circuit breakers use a microcontroller and one ADC to performboth the ground fault sampling and the arc fault sampling. However,while ground-fault sampling and grounded-neutral fault sampling may takeplace during separate time intervals, arc fault sampling can overlapwith both ground-fault and grounded-neutral fault sampling. Such overlapcan create conflicts requiring stringent timing constraints as well asother conflict avoidance measures in the microcontroller.

As an example, some dual function circuit breakers employ a complexscheme involving time slicing where the microcontroller allocates accessto the ADC according to a precise schedule for the required samplings.In this scheme, the ADC is shared among multiple detection algorithms,each running in its own detection interval and each requiring differentsequences of sensor signals to be sampled. Multiple priority-nestedinterrupts, timers, and state machines are needed to control programflow in such a scheme, which can render operation of the differentdetection algorithms less deterministic and more difficult to maintain.

Accordingly, what is needed is a way to minimize or eliminate timing andresource conflicts in a dual function CAFI/GFCI circuit breaker.

SUMMARY OF THE INVENTION

The disclosed embodiments provide a method and system for performing arcfault and ground fault detection in a dual function CAFI/GFCI circuitbreaker that can minimize or eliminate timing and resource conflicts.The method and system provide a dual function circuit breaker that usestwo separate ADCs, one for performing sampling with respect to arc faultdetection and one for performing sampling with respect to ground-faultand grounded-neutral fault detection. Each ADC operates independently ofthe other ADC and may be accessed by a controller as needed withoutinterfering with operation of the other ADC. Such simultaneous use ofmultiple ADCs minimizes or eliminates the need for complex time slicingand similar control schemes, thus freeing the controller for otheroperations and fault detection related tasks.

In some embodiments, the ADCs may be in the form of individual ADCmodules integrated or otherwise embedded within the controller, whichmay be a microcontroller, FPGA, ASIC, and the like. Each of the ADCmodules may be dedicated to sampling a different fault sensor of thecircuit breaker. For example, one ADC module may have its input channelconnected to an arc fault sensor while the other ADC module may have itsinput channel connected to a ground fault sensor. Each ADC module may beconfigured to sample its sensor at a different sampling frequencydepending on the needs of the respective detection algorithms. Thisallows each ADC module to run independently and in parallel with theother ADC module, thus providing greater flexibility for the controller.

In some embodiments, when an ADC module has finished sampling its faultsensor according to its respective sampling frequency, a softwareinterrupt may be triggered to store digital data resulting from thesampling in a buffer for subsequent use by the microcontroller.Alternatively, a direct memory access (DMA) module may be provided inthe microcontroller that can directly access and obtain the resultingdigital data from the ADC modules and store the data for subsequent useby the microcontroller.

In embodiments where each ADC module is configured to sample a singleground fault or arc fault sensor, the ADC module may have a single inputand a single output, as in the case of a single-pole circuit breaker. Insome embodiments, however, each ADC module may be configured to samplemultiple ground fault sensors or multiple arc fault sensors, as in thecase of a multi-pole circuit breaker. In these embodiments, each ADCmodule may have two or more inputs and two or more outputs that are used(or not used) as needed. It is also possible to have a third ADC module,for example, in order to divide up the ground fault sampling intoseparate ground-fault sampling and grounded-neutral fault sampling, orto perform some other operation in support of the single-pole ormulti-pole circuit breaker.

In some embodiments, instead of ADC modules that are integrated orembedded in the microcontroller, the ADC modules may be provided asseparate components that are external to the microcontroller. If used,the external ADC modules may interface to or otherwise communicate withthe DMA module instead of the microcontroller in these embodiments.Alternatively, a combination of integrated and external ADC modules mayalso be used.

In general, in one aspect, the embodiments disclosed herein relate todual function circuit breaker comprising a controller programmed todetect arc faults and ground faults. The dual function circuit breakeralso comprises a first ADC module accessible by the controller andconfigured to perform sampling of an arc fault signal and a second ADCmodule accessible by the controller and configured to perform samplingof a ground fault signal. The dual function circuit breaker furthercomprises an arc fault sensor configured to provide the arc fault signalto the first ADC module and a ground fault sensor configured to providethe ground fault signal to the second ADC module. The controller isprogrammed to access the first ADC module and the second ADC moduleindependently of each other to obtain data for detecting the arc faultsand ground faults, respectively.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other aspects of the disclosed embodiments will becomemore apparent from the following detailed description and the drawings,wherein:

FIG. 1 is an exemplary block diagram of a dual function circuit breakerin accordance with the embodiments disclosed herein;

FIG. 2 is an exemplary timing diagram for a dual function circuitbreaker in accordance with the embodiments disclosed herein;

FIG. 3 is an exemplary block diagram for an alternative dual functioncircuit breaker in accordance with the embodiments disclosed herein;

FIG. 4 is an exemplary block diagram for another alternative dualfunction circuit breaker in accordance with the embodiments disclosedherein;

FIG. 5 is an exemplary block diagram for yet another alternative dualfunction circuit breaker in accordance with the embodiments disclosedherein; and

FIG. 6 is an exemplary flow diagram for performing arc fault detection,ground-fault detection and grounded-neutral fault detection inaccordance with the embodiments disclosed herein.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

As an initial matter, it will be appreciated that the development of anactual, real commercial application incorporating aspects of thedisclosed embodiments will require many implementation-specificdecisions to achieve the developer's ultimate goal for the commercialembodiment. Such implementation-specific decisions may include, andlikely are not limited to, compliance with system-related,business-related, government-related and other constraints, which mayvary by specific implementation, location and from time to time. While adeveloper's efforts might be complex and time-consuming in an absolutesense, such efforts would nevertheless be a routine undertaking forthose of skill in this art having the benefit of this disclosure.

It should also be understood that the embodiments disclosed and taughtherein are susceptible to numerous and various modifications andalternative forms. Thus, the use of a singular term, such as, but notlimited to, “a” and the like, is not intended as limiting of the numberof items. Similarly, any relational terms, such as, but not limited to,“top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,”“side,” and the like, used in the written description are for clarity inspecific reference to the drawings and are not intended to limit thescope of the invention.

Referring now to FIG. 1, a microcontroller-based dual function CAFI/GFCIcircuit breaker 100 is shown in block diagram form according to theembodiments disclosed herein. The circuit breaker 100 shown here is asingle-pole circuit breaker, but those having ordinary skill in the artwill understand that the principles taught herein are also applicable tomulti-pole circuit breakers. As alluded to earlier, the dual functioncircuit breaker 100 is capable of detecting both ground faults and arcfaults without mutual interference or resource conflicts because it usesat least two ADC modules, one for performing ground fault sampling andone for performing arc fault sampling, as further discussed below. Thetwo ADC modules allow the circuit breaker 100 to schedule the samplingfor ground fault detection separately and independently from thesampling for arc fault detection. This helps the circuit breaker 100avoid the need to implement complex time slicing and similar controlschemes, thus freeing internal resources for other operations and faultdetection related activities.

As can be seen in FIG. 1, the dual function circuit breaker 100 may becomposed of a number of functional components, represented here byindividual blocks. Each block may of course be divided into severalconstituent blocks, or two or more blocks may be combined into a singleblock, without departing from the scope of the disclosed embodiments. Inthis embodiment, the dual function circuit breaker 100 may include aground fault current transformer 102, a ground fault sense signalconditioning circuit 104, and a test circuit 106, which may be apush-to-test circuit operable to provide a load and a step signal fortesting purposes. These components together form a ground fault sensecircuit 108 acting as a ground fault sensor when arranged as shown. Alsopresent are a current sensor 110, one or more bandpass filters 112, anintegrator 114, and a line voltage sensor 116. These components togetherform an arc fault sense circuit 118 acting as an arc fault sensor whenarranged as shown.

The use of the foregoing components for ground fault and arc faultdetection is well known in the art and therefore only a high-leveldescription of their specific functions will be provided below. Ingeneral operation, a controller 120 in the dual function circuit breaker100 receives the signals from the ground fault sense circuit 108 and thearc fault sense circuit 118 to detect ground faults and arc faults,respectively. The controller 120 may be any suitable controller known tothose having ordinary skill in the art, including a PIC16LF1554/9,PIC24FJ32GA002, or similar microcontroller from Microchip Technology,Inc., as well as a digital signal processor (DSP), an ASIC device, andthe like.

For the microcontroller 120 to process the signals from the ground faultsense circuit 108 and the arc fault sense circuit 118, the signals mustfirst be converted from continuous analog signals to discrete digitaldata. In accordance with the disclosed embodiments, the circuit breaker100 counterintuitively (and contrary to prevailing industry designstrategies) uses at least two dedicated ADC modules 122 (ADC 1) and 124(ADC 2) to receive and convert the signals from the ground fault sensecircuit 108 and the arc fault sense circuit 118, respectively, fromanalog signals to digital data. One of the ADC modules 122 or 124 may beembedded within the microcontroller 120 while the other ADC module 122or 124 may be external to the microcontroller 120. Alternatively, aswill be discussed later herein, both of the ADC modules 122 and 124 maybe embedded within the microcontroller 120 or both may be external tothe microcontroller 120.

In any case, the ADC modules 122 and 124 are designed to convert analogsignals to digital data and then provide the data to an arc fault andground fault detection unit 126 in the microcontroller 120 for furtherprocessing and fault detection. In the embodiment shown here, the firstADC module 122 (ADC 1) is configured to sample and convert ground faultsignals to digital data and the second ADC module 124 (ADC 2) isconfigured to sample and convert arc fault signals to digital data. Inalternative embodiments, the roles of the two ADC modules 122 and 124may be reversed. The arc fault and ground fault detection unit 126detects whether an arc fault, ground-fault, or grounded-neutral faulthas occurred based on the digital data from the ADC modules 122 and 124,respectively, and activates a current interrupt or trip circuit 128accordingly. The fault detections may be synchronized to or initiated bya zero-crossing signal from a line voltage zero-crossing detector 130that detects an alternating current (AC) zero crossing made by thesupply line (not expressly shown).

Other components that may be present in the circuit breaker 100 includea comparator 132 in the microcontroller 120 that receives the signalfrom the ground fault sense circuit 108 and compares it to aprogrammable voltage reference 134 (Vref) for purposes of ground faultsensor testing. As well, the microcontroller 120 may include one or moretimers 136 for keeping track of time and for driving peripheral devicesas needed, an input capture module 138 for providing timestamps astriggered by the comparator 132, one or more output compare modules 140for automating the ground fault sensor testing, and a ground faultsensor test control 142 for controlling the timing of a step signal thatmay be applied to the ground fault signal conditioning circuit 104 viathe test circuit 106.

The use of two ADC modules with one microcontroller, whileunconventional, provides several advantages over more mainstreamsolutions, such as a single-microcontroller/single-ADC solution. Forexample, having two ADC modules provides much more flexibility withrespect to the sampling rate for the signals from the ground fault sensecircuit 108 and the arc fault sense circuit 118. With a single-ADCsolution, time slicing must be implemented, which limits the samplingrate for each signal to a small range of possible frequencies that arecompatible with the sampling rate of the other signal in order to allowtime slicing of the ADC resource. However, with a dual ADC approach,sampling of the signals from the ground fault sense circuit 108 and thearc fault sense circuit 118 may take place independently and inparallel, which allows one or both sampling frequencies to besignificantly faster or slower compared to a single-ADC solution.

Having dual dedicated ADC modules also gives programmers more leeway interms of the design and functionality of the ground fault and arc faultdetection algorithms. For example, the dual ADC modules allows greaterpartitioning and/or separation of the ground fault and arc faultdetection algorithms within the firmware of the microcontroller 120,which may provide greater robustness and maintainability of thefirmware. In contrast, a single-microcontroller/single-ADC solution maycreate additional complications in product design as a result of thetime slicing scheme mentioned above and other resource sharingconflicts.

As well, having at least two ADC modules reduces overall microcontrollerutilization, as the microcontroller 120 would otherwise need toreconfigure a single ADC for different sampling schemes depending onwhether the ground fault sensor signal or the arc fault sensor signalneeds to be sampled, as would be the case with asingle-microcontroller/single-ADC solution. In a similar manner, the useof independent sampling frequencies for each ADC module may also improveoverall power consumption and lower heat output in the circuit breaker100. For example, one ADC module may be disabled or put into sleep modeafter sampling is finished without affecting the operation of the otherADC module. When the other ADC module is finished sampling, it maylikewise be disabled or put into sleep mode such that both ADC modulesmay be disabled or sleeping at the same time for a certain amount oftime. As well, one or both ADC modules may be disabled or put into sleepmode for a longer period of time and thus consume less power overallcompared to a single-microcontroller/single-ADC solution, where one ADCperforms all the sampling.

The use of at least two ADC modules, particularly with a singlemicrocontroller, also enables redundancy in sampling. For example, insome embodiments, it may be desirable to configure both ADC modules forsampling the same fault sensor signal or signals for purposes ofdetecting a failure in one of the ADC modules. In these embodiments,sampling may be performed on the same ground fault sensor signal by bothADC modules at substantially the same time, and/or sampling may beperformed on the same arc fault sensor signal by both ADC modules atsubstantially the same time. The results from the ADC modules may thenbe compared to determine if there are potential problems internally toeither of the ADC modules. Such redundant sampling would not be feasiblein a single-microcontroller/single-ADC solution.

Turning now to FIG. 2, a pair of timing diagrams 200 and 202 is shownillustrating some of the advantages of using two ADC modules 122 and124. Each timing diagram 200 and 202 is synchronized to or initiated bya zero-crossing interrupt signal (“ZX Interrupt”), which may be issuedby the zero crossing detector 130 (see FIG. 1) based on detection of asupply line zero crossing. Each timing diagram 200 and 202 is alsosectioned into a series of sampling intervals, Sampling Interval 1 andSampling Interval 2, respectively, within which sampling is performed bythe respective ADC module 122 and 124. The lengths of the samplingintervals are defined by timer interrupt signals, TMR 1 Interrupt andTMR 2 Interrupt, respectively, that may be issued by the one or moretimers 134 based on the specific sampling frequency used for each ADCmodule 122 and 124.

As can be seen, each ADC module 122 or 124 may have a sampling intervalthat is independent of (e.g., longer, shorter, same as) the samplinginterval of the other ADC module 122 or 124. In addition, each ADCmodule 122 or 124 may have a sampling duration, Sampling Duration 1 andSampling Duration 2, that is independent of (e.g., longer, shorter, sameas) the sampling duration of the other ADC module 122 or 124. Thisallows the ADC modules 122 and 124 to operate simultaneously and inparallel with one another with little risk of mutual interference orresource sharing conflicts. Consequently, the microcontroller 120 mayaccess and control each ADC module 122 or 124 independently of (e.g.,before, after, same time as) the other ADC module 122 or 124 with littlerisk of mutual interference or resource sharing conflicts. For example,the microcontroller 120 may reconfigure various parameters of each ADCmodule independently of the other ADC module, including samplingfrequency, data resolution, data format, voltage reference, channelconfiguration, DMA configuration, and the like. Similarly, themicrocontroller 120 may obtain data from each ADC module (i.e., read oneor more of the data registers therein) independently of the other ADCmodule. Likewise, the microcontroller 120 may start and stop each ADCmodule and/or service any interrupts from each ADC module independentlyof the other ADC module.

In the above embodiments, one ADC module 122 is embedded within themicrocontroller 120 while the other ADC module 124 is external to themicrocontroller 120. FIG. 3 depicts an alternative circuit breaker 300in which both ADC modules may be embedded within the microcontroller320. As can be seen, the circuit breaker 300 is otherwise the same asthe circuit breaker 100 of FIG. 1, except there are two ADC modules 302and 304 embedded in the microcontroller 320. Having both ADC modules 302and 304 embedded in the microcontroller 320 is advantageous in that theADC modules 302 and 304 do not take up space on the printed circuitboard.

FIG. 4 illustrates another alternative circuit breaker 400 in which adirect memory access (DMA) module may be used to access the ADC modules.As shown here, the circuit breaker 400 is otherwise the same as thecircuit breaker 300 of FIG. 3 insofar as there are two ADC modules 402and 404 embedded in the microcontroller 420. However, themicrocontroller 420 here may include an embedded DMA module 406 that candirectly access the ADC modules 402 and 404 and store the resulting datafor subsequent use by the microcontroller 420. The presence of the DMAmodule 406 frees the microcontroller 420 to perform other tasks withinthe circuit breaker 400 instead of accessing the ADC modules 402 and404.

FIG. 5 illustrates yet another alternative circuit breaker 500 in whicha DMA module may be used to access the ADC modules. In this embodiment,however, there are two external ADC modules 502 and 504 instead of anembedded ADC module in the microcontroller 520. The DMA module 506embedded in the microcontroller 520 may then be used to access theseexternal ADC modules 502 and 504. It is also possible to have anoptional third ADC module 508 (ADC 3) embedded in the microcontroller520, for example, in order to divide up the ground fault sampling intoseparate ground-fault sampling and grounded-neutral fault sampling, orto perform some other operation in support of the single-pole ormulti-pole circuit breaker.

In the foregoing embodiments, each of the two or more ADC modules isconfigured to sample a single ground fault or arc fault sensor such thateach ADC module may have a single input and a single output, as may bethe case with a single-pole circuit breaker. Examples of suchsingle-input/single-output ADC modules may include the MCP3001 andMCP3201 stand-alone ADC from Microchip Technology, Inc. In someembodiments, however, each of the two or more ADC modules may beconfigured to sample multiple ground fault sensors or multiple arc faultsensors, as may be the case with a multi-pole circuit breaker. In theselatter embodiments, each ADC module may have two or more inputs and twoor more outputs that are used (or not used) as needed. Examples of suchmulti-input/multi-output ADC modules may include the MCP3X02/4/8stand-alone ADC also from Microchip Technology, Inc. As well, thePIC16LF1554/9, PIC24FJ32GA002, and similar microcontrollers from thesame manufacturer have one or more built-in ADC modules that may beselectively operated as either single-input/single-output ormulti-input/multi-output.

Thus far, a number of specific implementations have been described for adual function circuit breaker according to the embodiments disclosedherein. Following now in FIG. 6 are general guidelines in the form of aflow chart 600 that may be used to implement one or more of theseembodiments. The flowchart 600 generally begins at block 602 where asupply line zero crossing is detected. This zero crossing initiates twoparallel sampling processes, an arc fault sampling process and a groundfault sampling process. As discussed above, each sampling process mayoccur independently of the other sampling process because each samplingprocess uses a separate ADC module from the other sampling process.

Thus, in one process, sampling of an arc fault sensor signal isperformed at block 604 using one of the ADC modules. A determination ismade at block 606 whether an arc fault has occurred based on thesampling of the arc fault sensor signal. If the determination is yes,then the circuit is interrupted at block 608. If the determination isno, then the flowchart 600 returns to block 602 to await another supplyline zero crossing.

In parallel with but independent of the above sampling process, samplesof a grounded-neutral fault sensor signal is performed at block 610. Adetermination is made at block 612 whether a grounded-neutral fault hasoccurred based on the sampling of the grounded-neutral fault sensorsignal. If the determination is yes, then the circuit is interrupted atblock 618. If the determination is no, then sampling of a ground-faultsensor signal is performed at block 614. A determination is made atblock 616 whether a ground-fault has occurred based on the sampling ofthe ground-fault sensor signal. If the determination is yes, then thecircuit is again interrupted at block 618. If the determination is no,then the flowchart 600 returns to block 602 to await another supply linezero crossing.

While particular aspects, implementations, and applications of thepresent disclosure have been illustrated and described, it is to beunderstood that the present disclosure is not limited to the preciseconstruction and compositions disclosed herein and that variousmodifications, changes, and variations may be apparent from theforegoing descriptions without departing from the scope of the disclosedembodiments as defined in the appended claims.

what is claimed is:
 1. A dual function circuit breaker, comprising: acontroller programmed to detect arc faults and ground faults; a firstADC module accessible by the controller and configured to performsampling of an arc fault signal; a second ADC module accessible by thecontroller and configured to perform sampling of a ground fault signal;an arc fault sensor configured to provide the arc fault signal to thefirst ADC module; and a ground fault sensor configured to provide theground fault signal to the second ADC module; wherein the controller isprogrammed to access the first ADC module and the second ADC moduleindependently of each other to obtain data for detecting the arc faultsand ground faults, respectively.
 2. The dual function circuit breakeraccording to claim 1, further comprising a direct memory access (DMA)module, wherein the controller is configured to obtain the data from thefirst ADC module and the second ADC module through the DMA module. 3.The dual function circuit breaker according to claim 1, wherein thefirst ADC module and the second ADC module are single-input andsingle-output ADC modules.
 4. The dual function circuit breakeraccording to claim 1, wherein the first ADC module and the second ADCmodule are multi-input and multi-output ADC modules.
 5. The dualfunction circuit breaker according to claim 1, wherein the circuitbreaker is a dual function CAFI/GFCI circuit breaker.
 6. The dualfunction circuit breaker according to claim 1, wherein the first ADCmodule performs sampling using a different sampling frequency from thesecond ADC module.
 7. The dual function circuit breaker according toclaim 1, wherein the first ADC module performs sampling using adifferent sampling duration from the second ADC module.
 8. The dualfunction circuit breaker according to claim 1, wherein sampling of theground fault signal comprise sampling of a ground-fault signal andsampling of a grounded-neutral fault signal.
 9. The dual functioncircuit breaker according to claim 1, wherein the first ADC module andthe second ADC module are each configured to be disabled or put intosleep mode independently of one another upon completion of sampling. 10.The dual function circuit breaker according to claim 9, wherein thefirst ADC module and the second ADC module may be disabled or sleepingat the same time.
 11. The dual function circuit breaker according toclaim 1, wherein the first ADC module is further configured to provideredundant sampling of the arc fault signal.
 12. The dual functioncircuit breaker according to claim 1, wherein the second ADC module isfurther configured to provide redundant sampling of the ground faultsignal.